Pulse tube cryocooler

ABSTRACT

A pulse tube cryocooler used under a non-vacuum atmosphere, the pulse tube cryocooler includes a pressure wave generator configured to generate pressure wave in an operations gas; a first stage regenerator having a high temperature end connected to the pressure wave generator; a second stage regenerator having a high temperature end connected to the first stage regenerator; a first stage pulse tube having a high temperature end and a low temperature end, the high temperature end being connected to a first buffer tank, the low temperature end being connected to a low temperature end of the first stage regenerator; a second stage pulse tube having a high temperature end and a low temperature end, the high temperature end being connected to a second buffer tank, the low temperature end being connected to a low temperature end of the second stage regenerator; a first stage cooling stage provided in a position where the first stage regenerator and the first stage pulse tube are connected; and a second stage cooling stage provided in a position where the second stage regenerator and the second stage pulse tube are connected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to pulse tube cryocoolers, and more specifically, to a pulse tube cryocooler used under non-vacuum atmosphere such as a helium atmosphere.

2. Description of the Related Art

Recently, as techniques of a pulse tube and design of an MRI (magnetic resonance imaging) cryostat has been improved, it has become possible to regenerate helium gas by using a pulse tube cryocooler. Furthermore, there are a single-stage type and a multi-stage type in the pulse tube cryocoolers. For example, in a two-stage pulse tube cryocooler, a first stage is cooled at approximately 40 K and a second stage is cooled at approximately 4 K. In addition, since the pulse tube cryocooler has little vibration and causes less noise in an MRI signal, the pulse tube cryocooler is more preferable than a GM (Gifford-McMahon) cryocooler having mechanical vibration.

In the meantime, it is normal practice that a regenerator and a pulse tube are provided in parallel in the pulse tube cryocooler. In a case where the pulse tube cryocooler having the above-mentioned structure is provided in a cooling vessel of an MRI magnet, convection of helium gas filling the cooling vessel is formed between the regenerator and the pulse tube due to temperature difference of the regenerator and the pulse tube. Because of this, thermal loss (convection loss) is generated between the first stage and the second stage so that serious loss for cooling capacity may be generated in the pulse tube cryocooler.

PCT Patent Gazette No. WO 03/036207 A2 discusses about a problem of a conventional two-stage 4 K pulse tube and suggests a sleeve structure where a pulse tube assembly is surrounded and a heat insulation member is provided around the tube.

In addition, PCT Patent Gazette No. WO 03/036190 A1 suggests, as means for solving a problem of convection loss, a structure of a heat insulation sleeve is provided around the pulse tube and the regenerator so that convection loss by helium gas is reduced.

Furthermore, Japanese Laid-Open Patent Application Publication No. 2006-214717 suggests a pulse tube cryocooler shown in FIG. 1. The pulse tube cryocooler shown in FIG. 1 is a two-stage pulse tube cryocooler having a valve mechanism 2, a valve driving device 3, a compressor 5, a first-stage regenerator 7, a first stage pulse tube 10, a second stage regenerator 26, a second stage pulse tube 40, and others. In this two-stage pulse tube cryocooler, a first cooling stage 30 is cooled at approximately 40 K and a second cooling stage 25 is cooled at approximately 4 K.

In the substantially center position of the second stage pulse tube 40, a thermal bridge 31 is provided between the regenerators 7 and 26 and the second stage pulse tube 40. The thermal bridge 31 is configured to thermally connect the regenerators 7 and 26 and the second stage pulse tube 40. While only a single thermal bridge 31 is provided in the example shown in FIG. 1, plural thermal bridges 31 may be provided.

Under the above-mentioned structure, heat is transferred between the regenerators 7 and 26 and the second stage pulse tube 40, so that temperature differences between the regenerators 7 and 26 and the second stage pulse tube 40 are reduced. Thus, generation of the convection of the gas in the atmosphere where the pulse tube cryocooler between the regenerators 7 and 26 and the second stage pulse tube 40 occurs so that convection loss may be expected. A flow of gas when the convection is generated is indicated by an arrow A in FIG. 1, for the convenience of understanding.

As shown in FIG. 1, it is possible to reduce the temperature differences between the regenerators 7 and 26 and the second stage pulse tube 40 by providing the thermal bridge 31 configured to thermally connect the regenerators 7 and 26 and the second stage pulse tube 40, and thereby a certain degree of reduction of the convection loss can be achieved.

However, if the heat conduction of operations gas (for example, helium gas) is low, the temperature differences between the regenerators 7 and 26 and the second stage pulse tube 40 are still large. Accordingly, in this case, it is difficult to prevent the convection loss so that cooling a subject to be cooled of the pulse tube cryocooler is not influenced by the convection loss.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the present invention may provide a novel and useful pulse tube cryocooler solving one or more of the problems discussed above.

More specifically, the embodiments of the present invention may provide a pulse tube cryocooler whereby it is possible to prevent generation of convection loss due to convection of atmosphere gas even if it is operated under a non-vacuum atmosphere.

One aspect of the present invention may be to provide a pulse tube cryocooler used under a non-vacuum atmosphere, the pulse tube cryocooler including:

a pressure wave generator configured to generate pressure wave in an operations gas;

a first stage regenerator having a high temperature end connected to the pressure wave generator;

a second stage regenerator having a high temperature end connected to the first stage regenerator;

a first stage pulse tube having a high temperature end and a low temperature end, the high temperature end being connected to a first buffer tank, the low temperature end being connected to a low temperature end of the first stage regenerator;

a second stage pulse tube having a high temperature end and a low temperature end, the high temperature end being connected to a second buffer tank, the low temperature end being connected to a low temperature end of the second stage regenerator;

a first stage cooling stage provided in a position where the first stage regenerator and the first stage pulse tube are connected; and

a second stage cooling stage provided in a position where the second stage regenerator and the second stage pulse tube are connected;

wherein a heat exchanging part is provided in the second stage pulse tube and in a stage corresponding position corresponding to the first stage cooling stage; and

the heat exchanging part is configured to exchange heat with the operations gas flowing in the second stage pulse tube so that heat exchanger effectiveness in the stage corresponding position is higher than heat exchanger effectiveness in a portion other than the stage corresponding position.

Other objects, features, and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a related art pulse tube cryocooler;

FIG. 2 is a schematic view of a pulse tube cryocooler of a first embodiment of the present invention;

FIG. 3 is a schematic view showing an example where the pulse tube cryocooler of the first embodiment of the present invention is applied to an MRI cryostat;

FIG. 4 is a graph showing temperature characteristics of the pulse tube cryocooler of the first embodiment of the present invention in comparison with temperature characteristics of the related art pulse tube cryocooler;

FIG. 5 is a schematic view of a pulse tube cryocooler of a second embodiment of the present invention;

FIG. 6 is a schematic view of a pulse tube cryocooler of a third embodiment of the present invention;

FIG. 7 is a schematic view of a pulse tube cryocooler of a fourth embodiment of the present invention;

FIG. 8 is a schematic view of a pulse tube cryocooler of a fifth embodiment of the present invention;

FIG. 9 is a schematic view of a pulse tube cryocooler of a sixth embodiment of the present invention;

FIG. 10 is a schematic view of a pulse tube cryocooler of a seventh embodiment of the present invention;

FIG. 11 is a schematic view of a pulse tube cryocooler of an eighth embodiment of the present invention;

FIG. 12 is a schematic view of a pulse tube cryocooler of a ninth embodiment of the present invention;

FIG. 13 is a schematic view of a pulse tube cryocooler of a tenth embodiment of the present invention;

FIG. 14 is a schematic view of a pulse tube cryocooler of an eleventh embodiment of the present invention;

FIG. 15 is a schematic view of a pulse tube cryocooler of a twelfth embodiment of the present invention; and

FIG. 16 is a schematic view of a pulse tube cryocooler of a thirteenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description is given below, with reference to the FIG. 2 through FIG. 16 of embodiments of the present invention.

FIG. 2 is a schematic view of a pulse tube cryocooler 1A of a first embodiment of the present invention. FIG. 3 is a schematic view showing an example where the pulse tube cryocooler 1A of the first embodiment of the present invention is applied to an MRI cryostat.

First, a structure of the pulse tube cryocooler 1A is discussed with reference to FIG. 1.

The pulse tube cryocooler 1A includes a valve mechanism 2, a compressor 5, a first stage regenerator 7, a first stage pulse tube 10, a second stage regenerator 26, an orifice-buffer assembly body 28, a second pulse tube 40A, and others.

Helium gas is used as operations fluid in the pulse tube cryocooler 1A. On the way where the operations gas, as discussed below, flows in the regenerators 7 and 26 and the pulse tubes 10 and 40A, adiabatic expansion causes cooling to occur.

Mesh-type regenerative members (not shown in FIG. 2), for example, are stacked inside the first stage regenerator 7 and fill the first stage regenerator 7. A high temperature end part of the first stage regenerator 7 is connected to the valve mechanism 2 via a path 15. A low temperature end part of the first stage regenerator 7 is connected to the high temperature end part of the second stage regenerator 26 and connected to the low temperature end of the first stage pulse tube 10 via a path 16.

A regenerative member (not shown in FIG. 2) made of a magnetic material, for example, fills the second stage regenerator 26. The low temperature end part of the second stage regenerator 26 is connected to the low temperature end part of the second stage pulse tube 40A via a path 17.

Rectifiers 9 and 11 are provided at the low temperature end part and the high temperature end part of the first stage pulse tube 10. The high temperature end part of the first stage pulse tube 10 is connected to the first buffer tank 14 via the orifice 12. In addition, a pipe connecting the first stage pulse tube 10 and the first buffer tank. 14 is connected to a path 15 via the orifice 13.

A first stage cooling stage 30 is provided at the low temperature end part of the first stage regenerator 7 and the low temperature end part of the first stage pulse tube 10. The first stage cooling stage 30 is thermally connected to the first stage regenerator 7 and the first stage pulse tube 10. The first stage cooling stage 30 is cooled at approximately 40 K at the time when the pulse tube cryocooler 1A is driven. The path 16 connecting the first stage regenerator 7 and the first stage pulse tube 10 is formed in the first stage cooling stage 30.

The second stage pulse tube 40A, as discussed below, has a structure where a small diameter part 45 is formed between an upper part 41 and a lower part 42. Rectifiers 22 and 24 are provided at the high temperature end part and the low temperature end part, respectively, of the second stage pulse tube 40A. The high temperature end part of the second stage pulse tube 40A is connected to the second buffer tank 21 via the orifice 27. In addition, a pipe connecting the second stage pulse tube 40A and the second buffer tank 21 is connected to the path 15 via the orifice 20.

A second stage cooling stage 25 is provided at the low temperature end part of the second stage regenerator 26 and the low temperature end part of the second stage pulse tube 40A. The second stage cooling stage 25 is thermally connected to the second stage regenerator 26 and the second stage pulse tube 40A. The second stage cooling stage 25 is cooled at approximately 4 K at the time when the pulse tube cryocooler 1A is driven. The path 17 connecting the second stage regenerator 26 and the second stage pulse tube 40A is formed in the second stage cooling stage 25.

The high temperature end parts of the first stage regenerator 7, the first stage pulse tube 10 and the second stage pulse tube 40A are fixed to a high temperature side flange 51 (shown in FIG. 3 and not shown in FIG. 2) provided supporting the orifice-buffer assembly body 28. Furthermore, the valve mechanism 2 is provided on an upper part of the orifice-buffer assembly body 28 and the valve driving device 3 is provided on an upper part of the valve mechanism 2.

A switching valve (not shown) being driven by the valve driving device 3 is provided inside the valve mechanism 2. A low pressure gas line 4 from the compressor 5, a high pressure gas line 6 from the compressor 5, and the above-mentioned path 15 are connected to the switching valve.

By driving of the valve driving device 3, the switching valve performs a switching process between a state where the low pressure gas line 4 and the path 15 are connected to each other and a state where the high pressure gas line 6 and the path 15 are connected to each other.

FIG. 3 shows the example where the pulse tube cryocooler 1A of the first embodiment of the present invention is applied to an MRI cryostat.

The pulse tube cryocooler 1A is provided in a neck tube 61 provided in a cryostat housing 60 of the MRI cryostat. The neck tube 61 has an upper part 61A having a large diameter and a lower part 61B having a small diameter. A neck tube heat station 68 is provided between the upper part 61A and the lower part 61B. The neck tube heat station 68 is thermally connected to a radiation shield 64 of the cryostat housing 60.

A vessel 65 configure to receive an MRI magnet 67 is provided at a most-bottom part of the neck tube 61. Liquid helium configured to cool the MRI magnet 67 fills the vessel 65. Because of this, a portion above the liquid helium 66 of the neck tube 61 is filled with the helium gas 62 so that the pulse tube cryocooler 1A is used under the helium atmosphere.

When the pulse tube cryocooler 1A is provided on the neck tube 61, the first stage regenerator 7, the first stage pulse tube 10, and the upper part 41 of the second stage pulse tube 40A are positioned in the upper part 61A of the neck tube 61. In addition, the second stage regenerator 26 and the lower part 42 of the second stage pulse tube 40A are positioned in the lower part 61 b of the neck tube 61. Furthermore, a high temperature flange 51 is connected to the neck tube 61 by an O-ring 52 in a sealed manner so that the neck tube 61 is sealed.

Under this structure, the first stage cooling stage 30 is thermally connected to a neck tube heat station 68 so that a radiation shield 64 is cooled at approximately 40 K via the neck tube heat station 68. In addition, under this structure, the second stage cooling stage 25 is situated in a position adjacent to the liquid helium 66.

Accordingly, since the second stage cooling stage 25 is cooled at 4 K, namely cryogenic temperature, vaporized helium gas is cooled by the second stage cooling stage 25 so as to be liquefied, and drops down. Because of this, the MRI magnet 67 is always submerged in the liquid helium 66 and therefore the MRI magnet 67 is securely cooled. The outside of the neck tube 61 is in a vacuum state 63.

Thus, since the pulse tube cryocooler 1A is provided at the neck tube 61 in this example, even if it is necessary to remove the pulse tube cryocooler 1A from the MRI cryostat due to the maintenance, it is possible to easily accommodate this.

Here, a small diameter part 45 provided at the second stage pulse tube 40A of the pulse tube cryocooler 1A is discussed. The small diameter part 45 (corresponding to a heat exchanging part in claims below) is formed in a body with the second stage pulse tube 40A in this example. This position corresponds to a position where the first stage cooling stage 30 is provided and is called a stage corresponding position in the explanation below. A cross-section S1 of the small diameter part 45, namely the cross-section where the operations gas flows, is smaller than the cross section S2 (where the operations gas flows) of a position other than the stage corresponding position of the second stage pulse tube 40A (S1<S2).

The length L of the small diameter part 45, namely the length L in a longitudinal direction of the second stage pulse tube 40A, is larger than the thickness W of the first stage cooling stage. More specifically, the length L of the small diameter part 45 has the following relationship with the thickness W of the first stage cooling stage 30.

0.8×W≦L≦1.20×W

It is desirable to set the following relation ship, especially.

0.95×W≦L≦1.05×W

Next, operations of the pulse tube cryocooler 1A having the above-discussed structure are discussed.

The pulse tube cryocooler 1A having the above-discussed structure drives a switching valve in the valve mechanism 2 by the valve driving device 3, and thereby connection of the path connected to the high temperature end part of the first stage regenerator 7 is selectively switched to the low temperature gas line 4 or the high temperature gas line 6.

Because of this, compression and expansion of the operations gas are repeated in the first stage pulse tube 10. By cooling generated due to this adiabatic expansion, the first stage cooling stage 30 provided at the low temperature end part of the first stage pulse tube 10 and the first stage regenerator 7 is cooled at approximately 40 K.

Furthermore, the pulse tube cryocooler 1A of this example has a two-stage type structure. Therefore, high pressure operations gas led from the compressor 5 into the first stage regenerator 7 via the high pressure gas line 6 is led from the low temperature end part of the first stage regenerator 7 to the high temperature end of the second stage regenerator 26.

In addition, the operations gas being led flows to the low temperature end part, while the operations gas performs heat exchange with the regenerative member, of the second stage regenerator 26, so as to pass through the communication tube 17 and flow into the low temperature end part of the second stage pulse tube 40A.

Under this structure, the operations gas already existing in the second stage pulse tube 40A is pushed by newly flowing operations gas so as to move to the high temperature end part. At the same time, operations gas passes through the orifice 20 and flows from the path 15 to the high temperature end part of the second stage pulse tube 40A so that flow of the operation gas from the low temperature end part of the second stage pulse tube 40A is prevented.

As a result of this, the timing of moving of the operations gas is delayed compared to the timing of pressure change in the second stage pulse tube 40A. After that, the pressure in the second stage pulse tube 40A becomes higher than the pressure in the second buffer tank 21 and thereby the operations gas in the second stage pulse tube 40A passes through the orifice and flows into the second buffer tank 21.

Next, the valve mechanism 2 is switched by the valve driving device 3. The path connected to the first stage regenerator 7 is switched so as to be connected to the low pressure gas line 4. As a result of this, pressure in the first stage regenerator 7 is decreased so that the operations gas in the second stage regenerator 26 is started being suctioned by the first stage regenerator 7. As a result of this, the operations gas already existing in the second stage pulse tube 40A is suctioned by the second stage regenerator 26 and thereby the operations gas in the second stage pulse tube 40A is started moving to the low temperature end part.

At the same time, operations gas passes through the orifice 20 and flows from the high temperature end part of the second stage pulse tube 40A to the path 15 so that flow of the operation gas from the low temperature end part of the second stage pulse tube 40A is prevented.

After that, the operations gas in the second buffer tank 21 passes through the orifice 27 and returns to the second stage pulse tube 40A, and the operations gas in the second stage pulse tube 40A flows to the low temperature end part of the second stage regenerator 26 and moves to the high temperature end part while cooling the regenerative member not shown. The operations gas returns to the compressor 5 via the first step regenerator 7, the path 15, the valve mechanism 2, and the low pressure gas line 4.

Thus, in the second stage pulse tube 40A, compression and expansion of the operations gas cooled at approximately 40 K by the first stage pulse tube 10 are repeated. Cooling generated by the adiabatic expansion is accumulated at the low temperature end parts of the second stage pulse tube 40A and the second stage regenerator 26.

As a result of this, the second stage cooling stage 25 provided at the low temperature end parts of the second stage pulse tube 40A and the second stage regenerator 26 is cooled at approximately 4K. Accordingly, even if the liquid helium 66 shown in FIG. 22 is vaporized, the liquid helium 66 can be condensed by the second stage cooling stage 25 so that a state where the MRI magnet 67 is dipped in the liquid helium 66 can be always formed.

In the meantime, the pulse tube cryocooler 1A of this example has a structure where the small diameter part 45 is formed in the stage corresponding position of the second stage pulse tube 40A.

Thus, the small diameter part 45 being smaller than a position other than the stage corresponding position is provided at the second stage pulse tube 40A, so that turbulent flow is generated when the operations gas flows in the small diameter part 45. Due to the turbulent flow of this operations gas, good heat exchanging is performed between the operations gas and a forming part of the small diameter part 45 of the second stage pulse tube 40A.

In addition, the small diameter part 45 is thermally connected to the first stage cooling stage 30. The operations gas flowing from the high temperature end part of the second stage pulse tube 40A passes through the small diameter part 45 so as to be cooled by the first stage cooling stage 30. In addition, as discussed above, since thermal efficiency of the small diameter part 45 is better than that of other parts, the stage corresponding position of the second stage pulse tube 40A can be cooled by the cooled operations gas more than other parts.

Next, action and effect by providing the small diameter part 45 at the second stage pulse tube 40A are discussed with reference to FIG. 4.

FIG. 4 is a graph showing temperature characteristics of the pulse tube cryocooler of the first embodiment of the present invention in comparison with temperature characteristics of the related art pulse tube cryocooler. More specifically, FIG. 4 shows temperatures at from the low temperature end part to the high temperature end part of the second stage pulse tube 40A. The horizontal axis of the graph indicates distance from the low temperature end part of the second stage pulse tube 40A. Positions PO through P3 shown in FIG. 1 correspond to positions P0 through P3 shown in FIG. 2.

“A” shown in FIG. 4 indicated temperature distribution of the first stage regenerator 7 and the second stage regenerator 26. In addition, “B” shown in FIG. 4 indicates the temperature distribution of the second stage pulse tube 40 of a pulse tube cryocooler having a structure where the thermal bridge 31 is removed from the pulse tube cryocooler shown in FIG. 1 as a related art case. Furthermore, “C” shown in FIG. 4 indicates the temperature distribution of the second stage pulse tube cryocooler 40 of the pulse tube cryocooler shown in FIG. 1 as a related art case. In addition, “D” shown in FIG. 4 indicates temperature distribution of the second stage pulse tube 40A of the pulse tube cryocooler having a structure where the small diameter part 45 is provided at the second stage pulse tube 40A of this example.

Referring to the temperature distribution of the first stage regenerator 7 and the second stage regenerator 26, the temperature in a position P0 that is the low temperature end part of the second stage regenerator 26 is approximately 4K. As the position is moved toward the high temperature end part from the position P0, the temperature of the first stage regenerator 7 and the second stage regenerator 26 are increased more.

However, the temperature of the first stage regenerator 7 and the second stage regenerator 26 at the positions P1 and P2 corresponding to the stage corresponding positions are maintained at a substantially constant temperature, namely approximately 40 K. This is because the stage corresponding position is a position where the first stage cooling stage 30 is provided and the first stage cooling stage 30 is cooled at approximately 40 K.

As the position is moved toward the high temperature end part from the position P2, the temperature of the first stage regenerator 7 and the second stage regenerator 26 are gradually increased more. Therefore, the temperature distribution A of the first stage regenerator 7 and the second stage regenerator 26 has characteristics of a step part provided in the stage corresponding position.

Referring to the temperature distributions B and C of the second stage pulse tube 40 of the related art, the temperature distribution B of the second stage pulse tube 40 not having the thermal bridge 31 is closer to the temperature distribution A of the first stage regenerator 7 and the second stage regenerator 26 than the temperature distribution C of the second stage pulse tube 40 having the thermal bridge 31. Accordingly, it is possible to make the temperature distribution C of the second stage pulse tube 40 closer to the temperature distribution A of the first stage regenerator 7 and the second stage regenerator 26 by providing the thermal bridge 31 than by not providing the thermal bridge 31. Therefore, it is possible to reduce the loss of convection.

However, in the related art pulse tube cryocooler having the temperature distributions B and C, the second stage pulse tube 40 has the same structure from the low temperature end part to the high temperature end part. Accordingly the temperature distribution has a linear functional property and a substantially straight line property.

On the other hand, the temperature distribution A of the first stage regenerator 7 and the second stage regenerator 26 has a property where the step part is formed in the stage corresponding position. Because of this, in the first stage regenerator 7, the second stage regenerator 26, and the second stage pulse tube 40 of the related art pulse tube cryocooler, an extremely large temperature difference is generated in the stage corresponding position so that it may not be possible to effectively prevent loss of convection.

On the other hand, in the pulse tube cryocooler 1A of this example, the small diameter part 45 is provided at the second stage pulse tube 40A. Hence, it is possible to cool the stage corresponding position of the second stage pulse tube 40A more than other positions.

Because of this, the temperature distribution D of the second stage pulse tube 40A of this example has a step part formed at parts corresponding to positions P1 and P2 as well as the temperature distribution A of the first stage regenerator 7 and the second stage regenerator 26.

Thus, by providing the small diameter part 45 at the second stage pulse tube 40A, it is possible to make the temperature distribution D of the second stage pulse tube 40A close to the temperature distribution A of the first stage regenerator 7 and the second stage regenerator 26. Hence, even if the pulse tube cryocooler 1A is used in a non-vacuum atmosphere such as helium atmosphere, it is possible to securely prevent the loss of convection due to temperature difference between the first stage regenerator 7 and the second stage regenerator 26 and the second stage pulse tube 40A so that cooling efficiency of the pulse tube cryocooler 1A can be improved.

On the other hand, the decrease of temperature of the second stage pulse tube 40A at the small diameter part 45 can be adjusted by the length of the small diameter part 45. In other words, by making the small diameter part 45 longer, a part having higher effectiveness as a regenerator exists longer so that the cooling efficiency is improved and a cooling state can be formed.

In addition, as discussed above, the purpose of cooling by the small diameter part 45 is making the temperature at the stage corresponding position of the second stage pulse tube 40A be close to the temperature of the stage corresponding position of the first stage regenerator 7 and the second stage regenerator 26. In order to realize this, according to experiments by the inventors of the present invention, it is preferable that the length L of the small diameter part 45 and the thickness W of the first stage cooling stage 30 be set to have the following relationship.

0.8×W≦L≦1.20×W

It is desirable to set the following relationship, especially, so that a more preferable effect can be achieved.

0.95×W≦L≦1.05×W

FIG. 5 is a schematic view of a pulse tube cryocooler 1B of a second embodiment of the present invention. In FIG. 5, parts that are the same as the parts shown in FIG. 2 and FIG. 3 are given the same reference numerals, and explanation thereof is omitted.

In the pulse tube cryocooler 1B of this example, a rectifier 70 is provided at the high temperature end part of the small diameter part 45 and a rectifier 71 is provided at the low temperature end part of the small diameter part 45. As discussed above, turbulent flow is generated in the small diameter part 45. While this turbulent flow is effective for improvement of the coefficient of heat transfer, this turbulent flow is not preferable from the perspective of maintaining the smooth flow of the operations gas in the second stage pulse tube 40A.

Because of this, in this example, the rectifiers 70 and 71 are provided so as to sandwich the small diameter part 45. As a result of this, the coefficient of heat transfer in the stage corresponding position is improved and the flow of the operations gas in a position other than the stage corresponding position can be smooth.

FIG. 6 is a schematic view of a pulse tube cryocooler 1C of a third embodiment of the present invention. In FIG. 6 through FIG. 16, parts that are the same as the parts shown in FIG. 2 and FIG. 5 are given the same reference numerals, and explanation thereof is omitted.

The pulse tube cryocooler 1C of the third embodiment of the present invention includes a single hole plug 80 as a heat exchanging part for improving cooling efficiency of the stage corresponding position of the second stage pulse tube 40B.

This single hole plug 80 is inserted and fit into the inside of the stage corresponding position of the second stage pulse tube 40B. In addition, a single flow hole 81 where the operations gas flows is formed inside the single hole plug 80. This operations gas generates turbulent flow when the operations gas passed through the flow hole 81. Therefore, in the third embodiment as well as the first embodiment, the second stage pulse tube 40B can be cooled at the single hole plug 80 so that loss of the convection can be prevented.

FIG. 7 is a schematic view of a pulse tube cryocooler 1D of a fourth embodiment of the present invention.

While a basic structure of the pulse tube cryocooler 1D is the same as that of the pulse tube cryocooler 1C of the third embodiment, a rectifier 70 is provided at the high temperature end part of the single hole plug 80 and a rectifier 71 is provided at the low temperature end part of the single hole plug 80 in the pulse tube cryocooler 1D. By providing the rectifiers 70 and 71 so that the single hole plug 80 is sandwiched by the rectifiers 70 and 71, it is possible to improve the coefficient of heat transfer in the stage corresponding position and make the flow of the operations gas in the position other than the stage corresponding position smooth.

FIG. 8 is a schematic view of a pulse tube cryocooler 1E of a fifth embodiment of the present invention.

In the pulse tube cryocooler 1E of the fifth embodiment, a multi-hole plug 90 is provided as a heat exchanging part for improving the cooling efficiency in the stage corresponding position of the second stage pulse tube 40B. This multi-hole plug 90 is inserted in the stage corresponding position of the second stage pulse tube 40 as shown in FIG. 8(A).

In addition, as shown in FIG. 8(B), a large number of flow holes 91 are formed in the multi-hole plug 90 so that the operations gas flows. When the operations gas passes through the large number of flow holes 91, the operations gas generates the turbulent flow so that the second stage pulse tube 40B can be cooled at the multi-hole plug 90 and thereby the loss of convection can be prevented in this embodiment as well as the first embodiment.

FIG. 9 is a schematic view of a pulse tube cryocooler 1F of a sixth embodiment of the present invention.

While a basic structure of the pulse tube cryocooler 1F is the same as that of the pulse tube cryocooler 1E of the fifth embodiment, a rectifier 70 is provided at the high temperature end part of the multi-hole plug 90 and a rectifier 71 is provided at the low temperature end part of the multi-hole plug 90 in the pulse tube cryocooler 1D. By providing the rectifiers 70 and 71 so that the multi-hole plug 90 is sandwiched by the rectifiers 70 and 71, it is possible to improve the coefficient of heat transfer in the stage corresponding position and make the flow of the operations gas in the position other than the stage corresponding position smooth.

FIG. 10 is a schematic view of a pulse tube cryocooler 1G of a seventh embodiment of the present invention.

In the pulse tube cryocooler 1G, a mesh plug 120 is provided as a heat exchanging part for improving the cooling efficiency in the stage corresponding position of the second stage pulse tube 40B. This mesh plug 120 is inserted in the stage corresponding position of the second stage pulse tube 40B. When the operations gas passes through the mesh plug 120, the operations gas generates the turbulent flow so that the second stage pulse tube 40B can be cooled at the mesh plug 120 and thereby the loss of convection can be prevented in this embodiment as well as the first embodiment.

FIG. 11 is a schematic view of a pulse tube cryocooler 1H of an eighth embodiment of the present invention.

In the pulse tube cryocooler 1H, a connecting member 130 having a flow hole 131 is provided as a heat exchanging part for improving the cooling efficiency in the stage corresponding position of the second stage pulse tube 40C.

In this example, the second stage pulse tube 40C has an upper part pulse tube 43, a lower part pulse tube 44, and a connecting member 130. The upper part pulse tube 43 and the lower part pulse tube 44 are connected to the connecting parts 132 and 133, respectively, of the connecting member 130.

More specifically, a low temperature end part of the upper part pulse tube 43 is connected to the connecting part 132 at the high temperature part of the connecting member 130, and a high temperature end part of the lower part pulse tube 44 is connected to the connecting part 133 at the low temperature part of the connecting member 130.

Thus, in this example, since the upper part pulse tube 43 and the lower part pulse tube 44 are separated from each other, it is possible to easily connect the upper part pulse tube 43 and the lower part pulse tube 44 to the connecting member 130. In addition, when the operations gas passes through the flow hole 131 formed in the connecting member 130, the operations gas generates the turbulent flow so that the second stage pulse tube 40C can be cooled at the flow hole 131 and thereby the loss of convection can be prevented in this embodiment as well as the first embodiment.

FIG. 12 is a schematic view of a pulse tube cryocooler 1I of a ninth embodiment of the present invention.

While a basic structure of the pulse tube cryocooler 1I is the same as that of the pulse tube cryocooler 1H of the eighth embodiment, a rectifier 70 is provided at the low temperature end part of the upper part pulse tube 43 and a rectifier 71 is provided at the high temperature end part of the lower part pulse tube 44 in the pulse tube cryocooler 1I. By providing the rectifiers 70 and 71 so that the connecting member 130 is sandwiched by the rectifiers 70 and 71, it is possible to improve the coefficient of heat transfer in the stage corresponding position and make the flow of the operations gas in the position other than the stage corresponding position smooth.

FIG. 13 is a schematic view of a pulse tube cryocooler 1J of a tenth embodiment of the present invention.

In the pulse tube cryocooler 1J, a small diameter part 141 is provided as a heat exchanging part for improving the cooling efficiency in the stage corresponding position of the second stage pulse tube 40C. The small diameter part 141 is formed in the first stage cooling stage 140.

In this example, the second stage pulse tube 40C has an upper part pulse tube 43 and a lower part pulse tube 44. The upper part pulse tube 43 and the lower part pulse tube 44 are connected to each other by a small diameter part 141 formed in the first stage cooling stage 140.

More specifically, a low temperature end part of the upper part pulse tube 43 is connected to the high temperature part of the small diameter part 141 formed in the first stage cooling stage 140. In addition, a high temperature end part of the lower part pulse tube 44 is connected to the low temperature part of the small diameter part 141 formed in the first stage cooling stage 140.

Thus, in this example, since the upper part pulse tube 43 and the lower part pulse tube 44 are separated from each other, it is possible to easily connect the upper part pulse tube 43 and the lower part pulse tube 44 to the connecting member 140. In addition, when the operations gas passes through the small diameter part 141, the operations gas generates the turbulent flow so that the second stage pulse tube 40C can be cooled at the small diameter part 141 and thereby the loss of convection can be prevented in this embodiment as well as the first embodiment.

In addition, the first stage regenerator 7, the second stage regenerator 26, and the second stage pulse tube 40D are thermally connected to each other in the stage corresponding position by the first stage cooling stage 140. Therefore, the temperatures of the stage corresponding position of the first stage regenerator 7, the second stage regenerator 26, and the second stage pulse tube 40D can be made close to each other, and therefore it is possible to securely prevent the loss of convection.

FIG. 14 is a schematic view of a pulse tube cryocooler 1K of an eleventh embodiment of the present invention.

While a basic structure of the pulse tube cryocooler 1K is the same as that of the pulse tube cryocooler 1J of the tenth embodiment, a rectifier 70 is provided at the high temperature end part of the small diameter part 141 and a rectifier 71 is provided at the low temperature end part of the small diameter part 141. By providing the rectifiers 70 and 71 so that the small diameter part 141 is sandwiched by the rectifiers 70 and 71, it is possible to improve the coefficient of heat transfer in the stage corresponding position and make the flow of the operations gas in the positions other than the stage corresponding position smooth.

FIG. 15 is a schematic view of a pulse tube cryocooler 1L of a twelfth embodiment of the present invention.

In the pulse tube cryocooler 1L, a small diameter part 141 at the first stage cooling stage 140 and a bypass path 150 connecting the small diameter part 141 and the first stage regenerator 7 are provided as heat exchanging parts for improving the cooling efficiency in the stage corresponding position of the second stage pulse tube 40C.

Thus, by connecting the small diameter part 141 to the first stage regenerator 7 by the bypass path 150, a small amount of operations gas flows by the bypass path 150. Because of this, it is possible to make temperatures of the first stage regenerator 7 and the second stage pulse tube 40E at the connecting position close to each other. Hence, it is possible to securely prevent the loss of convection.

FIG. 16 is a schematic view of a pulse tube cryocooler 1M of a thirteenth embodiment of the present invention.

While a basic structure of the pulse tube cryocooler 1M is the same as that of the pulse tube cryocooler 1L of the twelfth embodiment, a rectifier 70 is provided at the high temperature end part of the small diameter part 141 and a rectifier 71 is provided at the low temperature end part of the small diameter part 141. By providing the rectifiers 70 and 71 so that the small diameter part 141 is sandwiched by the rectifiers 70 and 71, it is possible to improve the coefficient of heat transfer in the stage corresponding position and make the flow of the operations gas in the positions other than the stage corresponding position smooth.

Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.

In other words, in the above-discussed embodiments, as heat exchanging parts for improving the cooling efficiency in the stage corresponding position of the second stage pulse tubes, the single hole plug 80, the multi-hole plug 90, the mesh plug 120, the connection member 130, and the small diameter part 141 are provided. The length L of the heat exchanging parts 80, 90, 120, 130, and 140 have the following relationship with the thickness W of the first stage cooling stage 30.

0.8×W≦L≦1.20×W.

It is desirable to set the following relationship, especially.

0.95×W≦L≦1.05×W

While the pulse tube cryocoolers 1A through 1M are provided in the helium atmosphere in the above-discussed embodiments, a non-vacuum atmosphere is not limited to the helium atmosphere. The pulse tube cryocoolers 1A through 1M may be provided in the atmosphere including at least one of gas selected from a group consisting of hydrogen and neon.

Thus, according to the embodiments of the present invention, it is possible to provide a pulse tube cryocooler used under a non-vacuum atmosphere, the pulse tube cryocooler including: a pressure wave generator configured to generate pressure wave in an operations gas; a first stage regenerator having a high temperature end connected to the pressure wave generator; a second stage regenerator having a high temperature end connected to the first stage regenerator; a first stage pulse tube having a high temperature end and a low temperature end, the high temperature end being connected to a first buffer tank, the low temperature end being connected to a low temperature end of the first stage regenerator; a second stage pulse tube having a high temperature end and a low temperature end, the high temperature end being connected to a second buffer tank, the low temperature end being connected to a low temperature end of the second stage regenerator; a first stage cooling stage provided in a position where the first stage regenerator and the first stage pulse tube are connected; and a second stage cooling stage provided in a position where the second stage regenerator and the second stage pulse tube are connected; wherein a heat exchanging part is provided in the second stage pulse tube and in a stage corresponding position corresponding to the first stage cooling stage; and the heat exchanging part is configured to exchange heat with the operations gas flowing in the second stage pulse tube so that heat exchanger effectiveness in the stage corresponding position is higher than heat exchanger effectiveness in a portion other than the stage corresponding position.

The heat exchanging part may have a structure where a flow path area of the stage corresponding position is smaller than a flow path area of the portion other than the stage corresponding position. The heat exchanging part may have a structure where a circulating hole is formed in a base part. The heat exchanging part may be made of a porous material. The length L in a longitudinal direction of the pulse tube of the heat exchanging part may have the following relationship with the thickness W of the first stage cooling stage. 0.8×W≦L≦1.20×W. Rectifiers may be provided in upper and lower positions sandwiching the heat exchanging part, the rectifiers being configured to rectify the flow of the operations gas. The non-vacuum atmosphere may include at least one of a gas selected from a group consisting of helium, hydrogen, and neon.

According to the embodiments of the present invention, the heat exchanging part having heat exchanger effectiveness higher than that of a part other than the stage corresponding position is provided in the stage corresponding position of the second stage pulse tube.

Therefore, good heat exchanging is performed by the heat exchanging part between the first stage cooling stage and the operations gas and between the operations gas and the second stage pulse tube. Hence, it is possible to make the temperature of the second stage pulse tube in the stage corresponding position close to the temperature of the regenerator. Because of this, even if the pulse tube cryocooler is used in the non-vacuum atmosphere, it is possible to prevent loss of convection due to the temperature difference between the second pulse tube cryocooler and the regenerator.

This patent application is based on Japanese Priority Patent Application No. 2007-113434 filed on Apr. 23, 2007, the entire contents of which are hereby incorporated by reference. 

1. A pulse tube cryocooler used under a non-vacuum atmosphere, the pulse tube cryocooler comprising: a pressure wave generator configured to generate pressure wave in an operations gas; a first stage regenerator having a high temperature end connected to the pressure wave generator; a second stage regenerator having a high temperature end connected to the first stage regenerator; a first stage pulse tube having a high temperature end and a low temperature end, the high temperature end being connected to a first buffer tank, the low temperature end being connected to a low temperature end of the first stage regenerator; a second stage pulse tube having a high temperature end and a low temperature end, the high temperature end being connected to a second buffer tank, the low temperature end being connected to a low temperature end of the second stage regenerator; a first stage cooling stage provided in a position where the first stage regenerator and the first stage pulse tube are connected; and a second stage cooling stage provided in a position where the second stage regenerator and the second stage pulse tube are connected; wherein a heat exchanging part is provided in the second stage pulse tube and in a stage corresponding position corresponding to the first stage cooling stage; and the heat exchanging part is configured to exchange heat with the operations gas flowing in the second stage pulse tube so that heat exchanger effectiveness in the stage corresponding position is higher than heat exchanger effectiveness in a portion other than the stage corresponding position.
 2. The pulse tube cryocooler as claimed in claim 1, wherein the heat exchanging part has a structure where a flow path area of the stage corresponding position is smaller than a flow path area of the portion other than the stage corresponding position.
 3. The pulse tube cryocooler as claimed in claim 1, wherein the heat exchanging part has a structure where a circulating hole is formed in a base part.
 4. The pulse tube cryocooler as claimed in claim 1, wherein the heat exchanging part is made of a porous material.
 5. The pulse tube cryocooler as claimed in claim 1, wherein the length L in a longitudinal direction of the pulse tube of the heat exchanging part has the following relationship with the thickness W of the first stage cooling stage. 0.8×W≦L≦1.20×W.
 6. The pulse tube cryocooler as claimed in claim 1, wherein rectifiers are provided in upper and lower positions sandwiching the heat exchanging part, the rectifiers being configured to rectify the flow of the operations gas.
 7. The pulse tube cryocooler as claimed in claim 1, wherein the non-vacuum atmosphere includes at least one of a gas selected from a group consisting of helium, hydrogen, and neon. 